The effects of histidyl-proline-diketopiperazine, a metabolite of TRH, on prolactin release by the rat pituitary gland in vitro.
The effect of four different preparations of histidyl-proline-diketopiperazine (DKP) on prolactin (PRL) release by rat hemipituitary glands and cultured dispersed normal pituitary cells was studies. Three DKP preparations )0.1-1 micrometer) were ineffective on PRL release in vitro. By combining the results from 12 incubation vials in 3 experiments 1 micrometer of the fourth DKP preparation was shown to suppress PRL release slightly but significantly by 18%, (P less than 0.05). DKP did not enhance the dopamine-mediated inhibition of PRL release and it also did not reverse the TRH-mediated stimulation of PRL release by the pituitary gland in vitro. It was concluded that DKP (in micromolar concentrations) has a very weak PRL release-inhibiting action and is probably not a physiologically acting prolatin-inhibiting factor.
D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D010456:Peptides, Cyclic / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism
D010456:Peptides, Cyclic; D010879:Piperazines; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; C015924:histidyl-proline diketopiperazine